1. Field of the invention:
This invention relates to a color television camera having one image pickup tube, and more particularly to a color television camera for generating color video signals with improved color reproducibility characteristics.
2. Description of the Prior Art:
One type of color television camera has three image pickup tubes for three primary colors. In this type of color television camera, light from an object to be televised is directed to an optical color separating system through a common camera lens, and the three color-separated images are focused onto the pickup tubes, respectively. FIG. 1 of the accompanying drawings shows in block form a typical entire arrangement of such a color television camera. The color television camera includes pickup tubes 1R, 1G and 1B onto which color-separated images are focused. The pickup tubes 1R, 1G and 1B then generate electric signals representative of the color components of the images. The output signals from the pickup tubes 1R, 1G and 1B are supplied through preamplifiers 2R, 2G and 2B and processing circuits 3R, 3G and 3B, respectively, to a matrix circuit 4. The matrix circuit 4 generates a luminance signal Y, a red color difference signal R-Y, and a blue color difference signal B-Y from the three primary color signals. The output signals from the matrix circuit 4 are supplied to a color encoder 5 which produces at an output terminal 6 a composite color television signal of the NTSC standard, for example. In the processing circuit 3R, 3G or 3B, each primary color signal is gamma-corrected and the excessive white level is clipped. According to this type of color television camera, when a bright red object is viewed by the camera, the level of the output signal from the pickup tube 1R is high. However, since this signal is supplied to the matrix circuit 4 after it has been gamma-corrected and clipped in its white level in the processing circuit 3R, the luminance signal Y and the red color difference signal have the proper levels, that is, the level of the luminance signal Y from the matrix circuit 4 is about 30% of the maximum luminance signal. With this prior art color television camera, however, the total cost is very high as three pickup tubes and an optical color separating system are required.
Color television cameras are also known which have a single pickup tube having red, green and blue stripe filters arranged at a predetermined pitch on a photoconductive layer of the tube. One such color television camera is shown in U.S. Pat. No. 3,688,020 assigned to the same assignee as the present invention. This type of color television camera requires only one tube with filter means, and hence is much less expensive than the earlier types of color television cameras. However, the single-tube color television camera is disadvantageous in that its color reproduction characteristics are not so good as those of the three-tube color television cameras. This is because the luminance signal, which is output from a low-pass filter, has a high level when the image of a bright red object is picked up, and the color components of the image are derived in the form of frequency-modulated signals or phase-modulated signals. Therefore, the level of the red color difference signal, even if it has been made proper, is still low relative to the luminance signal level. This shortcoming causes an image reproduced on the signals from the single-tube type camera to be deteriorated such that the red color is faded and its saturation appears to be decreased as compared with the actual color.